Given a directory with a subdirectory (and a couple of files in each level):
$ find mydir -printf '%y %p\n' d mydir f mydir/file1 f mydir/file2 d mydir/subdir f mydir/subdir/file3 f mydir/subdir/file4
Running a swh scanner scan -f ndjson on it, results in
$ swh scanner scan -f ndjson mydir {"mydir/subdir": {"swhid": "swh:1:dir:c8813fd1fd68cc3e5a49cc2f81c786116a7b5314", "known": false}} {"mydir/subdir/file3": {"swhid": "swh:1:cnt:f250008831e45d6c73f01b9d4f5085c2d1abb400", "known": true}} {"mydir/subdir/file4": {"swhid": "swh:1:cnt:2c09459acd4d0946c02b5d61bf2d279af395a15b", "known": true}} {"mydir/subdir/file3": {"swhid": "swh:1:cnt:f250008831e45d6c73f01b9d4f5085c2d1abb400", "known": true}} {"mydir/subdir/file4": {"swhid": "swh:1:cnt:2c09459acd4d0946c02b5d61bf2d279af395a15b", "known": true}} {"mydir/file1": {"swhid": "swh:1:cnt:f3d94808194a3f1c2c2e6ab4009c7cf2471a095b", "known": false}} {"mydir/file2": {"swhid": "swh:1:cnt:2834e5822e25b78ca17b20524a64febb26237c7a", "known": true}}
(note the duplicate lines for file3 and file4)
Reporting in colored output ("txt") or multi-line JSON (-f json) does not show this behavior.